A panoramic scene spans the entire 360 degree horizontal field of view. Panoramic images of scenes have important applications in computerized visualization. Panoramic images give the viewer an impression of being immersed in the scene.
A panoramic image can be generated by first taking a set of overlapping images of the scene while rotating a camera about a vertical axis which passes through the optical center of the camera. The set of images, if not already in digital form, can be digitized and processed to improve quality. The processed images can be projected onto a cylindrical surface for viewing. Alternatively, the images can be viewed using, for example, a head-mounted viewing device which simulates the cylindrical surface as the head is rotated. This virtually gives the viewer a sense of observing a real scene. In order to properly process and project the set of images, the focal length of the viewing system, e.g., the cross-sectional radius of the surface of the viewing cylinder, must substantially correspond to the focal length of the camera.
In the prior art, the focal length (.function.) of the camera is usually known. The focal length of the camera can be determined by calculating the distance between the image plane and the optical center of the camera. This can be done through the process of camera calibration.
Some calibration methods take images of calibration patterns such as regularly spaced dots or lines having known dimensions. Other methods take images of structures having constrained and known shapes, for example spheres or cubes. These methods have the disadvantage of requiring explicit feature extraction. In addition, these methods are not practical if the focal length of the camera is known to drift over time, or change with zooming or focussing.
In methods that involve a set of images taken while rotating the camera 360 degrees, feature tracking can be used on the set of images to recover the focal length. In some methods, translation estimates are made of a local area in the vicinity of the center of the images. This method requires small incremental steps while panning the camera. Another method requires explicit feature extraction, such as corners and edges, and tracking the features from one image to the next.
It is desired to automatically determine the focal length of a camera using a set of images without using special calibration set-ups and without explicit feature detection and tracking. Then, using the correct focal length, it becomes possible to create a panoramic view of the images that is both optically correct and seamlessly blended.